(1) Field of the Invention
The present invention relates to a technique for supplying power of a plurality of bus power supplies in, for example, an IBA (Intermediate Bus Architecture) power supply system.
(2) Description of Related Art
Recent trend toward voltage reduction/large current consumption of elements (load elements) causes fluctuations in voltage due to voltage drop in wiring. To suppress such the fluctuations in voltage, a power supply in POL (Point Of Load) system (hereinafter, referred to as POL power supply) tends to be used, in which the power supply is arranged very close to the elements, as noted in patent document 1 below.
To directly pull the power-feeding power supply on the primary side in the POL power supply prevents a reduction in size of the POL power supply and makes it difficult to secure insulation inside the apparatus. A known technique having overcome this problem is IBA (Intermediate Bus Architecture) power-feeding power supply, in which an insulated power supply for converting the voltage of the primary power-feeding power supply into a voltage (intermediate voltage, intermediate potential) lower than that of the primary power-feeding power supply is arranged in the preceding stage of a small-sized non-insulated power supply (POL converter), and a low-voltage power generated by this insulated power supply is supplied to the non-insulated power supply to decrease the insulation withstand voltage inside the apparatus.
In such an IBA power-feeding power supply configuration, the capacity of the insulated power supply for supplying the power to the non-insulated power supply is increased with an increase in electric power of the apparatus. For reasons that use of an insulated power supply having a lower height and a small-to-middle capacity agreeing with the height of outer dimensions of the load element can materialize a compact apparatus, and that combined use of the same type of the insulated power supply can realize improved economy rather than many types of the apparatus are manufactured, each in a small quantity, according to the load capacity, recent trend is combined use of a plurality of insulated power supplies having about 50 to 200 Watt output capacity, as the insulated power supply.
FIG. 11 is a diagram schematically showing an example of configuration of a power supply apparatus having a known IBA power-feeding power supply configuration.
In the example shown in FIG. 11, non-insulated power supplies DCDC13 to DCDC17 are arranged near load elements LOAD11 and LOAD12, a plurality (two in the example shown in FIG. 11) of insulated power supplies DCDC11 and DCDC12 are arranged in the preceding stage (in the upstream) of the non-insulated power supplies DCDC13 to DCDC17, wherein the power is fed from the insulated power supply 11 to the non-insulated power supply 13 and 14 and from the insulated power supply DCDC 12 to the non-insulated power supplies DCDC15 to DCDC17.
Generally, the load elements LOAD11 and LOAD12 require a plurality of power supplies such as a core power supply, an I/O power supply and the like. In the example shown in FIG. 11, the power is fed from the non-insulated power supply DCDC13 to a V1 terminal of the load element LOAD11 and from the non-insulated power supply DCDC 14 to a V2 terminal of the load element load11, while the power is fed from the non-insulated power supply DCDC 15 to a V1 terminal of the load element LOAD12 and from the non-insulated power supply DCDC16 to a V2 terminal of the load element LOAD12, and further the power is fed from the non-insulated power supply DCDC 17 to a V3 terminal of each of the load elements LOAD11 and LOAD12.
When the power consumption at the V3 terminals of the load elements LOAD11 and LOAD12 is small, it is general to supply the power from one non-insulated power supply DCDC17 to both the load elements LOAD11 and LOAD12.
[Patent Document 1] Japanese Patent Application Laid-Open Publication No. 2007-49822
However, when a plurality of the insulated power supplies DCDC11 and DCDC12 are used in combination in a power supply apparatus having such a known IBA feeding power supply configuration, it is unavoidable that variation in start-up of these plural insulated power supplies DCDC11 and DCDC12 occurs.
FIGS. 12(a) through 12(h) are a timing chart showing states of the voltages in the known power supply apparatus shown in FIG. 11. FIG. 12(a) is a diagram showing an intermediate voltage Vi11 outputted from the insulated power supply DCDC11. FIG. 12(b) is a diagram showing an intermediate voltage Vi12 outputted from the insulated power supply DCDC12. FIG. 12(c) is a diagram showing a signal inputted to the V1 terminal of the load element LOAD11. FIG. 12(d) is a diagram showing a signal inputted to the V2 terminal of the load element LOAD1. FIG. 12(e) is a diagram showing a signal inputted to the V3 terminal of the load element LOAD11. FIG. 12(f) is a diagram showing a signal inputted to the V1 terminal of the load element LOAD12. FIG. 12(g) is a diagram showing a signal inputted to the V2 terminal of the load element LOAD12. FIG. 12(h) is a diagram showing a signal inputted to the V3 terminal of the load element LOAD12.
In the case where the load elements LOAD11 and LOAD12 are both load elements that cannot normally operate unless the power sources V1 to V3 are simultaneously applied, if the insulated power supply DCDC11 (time T11; refer to point A in FIG. 12(a)) starts earlier than the insulated power supply DCDC12 (time T12; refer to point B in FIG. 12(b)), power supply from the insulated power supply DCDC11 to the non-insulated power supply DCDC13 and DCDC14 would be done earlier than power supply from the insulated power supply DCDC12 to the non-insulated power supplies DCDC15 to DCDC17, hence, in the load element LOAD11, a voltage is applied to the terminal V3 later than the terminal V1 (refer to point C in FIG. 12(c)) and the terminal V2 (refer to point D in FIG. 12(d)), which would prevent the load element LOAD11 from being able to operate normally.
In other words, in a load element requiring a plurality of power sources, if the plural power sources are not applied simultaneously or in the defined order, the load element would not operate normally.
Further, if inter-element signals are not transmitted simultaneously or in the predetermined order to the plural load elements, hangup or error would occur.
For these reasons, there has been proposed a method of connecting outputs of the plural insulated power supplies DCDC11 and DCDC12 in parallel to simultaneously supply the power to the non-insulated power supplies DCDC13 to DCDC17 in the following stage thereof.
FIG. 13 is a diagram schematically showing another example of configuration of the known power supply apparatus. FIGS. 14(a) and 14(b) are a timing chart showing states of voltages in the known power supply configuration shown in FIG. 13. FIG. 14(a) is a diagram showing a voltage Vi11 outputted from an insulated power supply DCDC11. FIG. 14(b) is a diagram showing a voltage Vi12 outputted from an insulated power source DCDC12.
In the known power supply apparatus shown in FIG. 13, outputs from +Vout terminals of the plural insulated power supplies DCDC11 and DCDC12 are connected in parallel and inputted to +Vin terminals of non-insulated power supplies DCDC13 to DCDC17 in the following stage. Whereby, the power is simultaneously supplied from the plural insulated power supplies DCDC11 and DCDC12 to the non-insulated power supplies DCDC13 to DCDC17 in the following stage.
However, the known method shown in FIG. 13 has a risk that when either one (the insulated power supply DCDC11 in the example shown in FIGS. 14(a) and 14(b)) of the insulated power supplies DCDC11 and DCDC12 starts earlier (refer to a time T11 in FIG. 14(a)), all the loads of the non-insulated power supplies DCDC13 to DCDC17 concentrate on the insulated power supply DCDC11 before the insulated power supply DCDC12 starts (refer to a time T12 in FIG. 14(b)), as a result, the insulated power supply DCDC11 goes down.